The present invention relates to a cleaning agent for the semiconductor substrate surface used in production steps of semiconductors and LCDs (liquid crystal displays), and further relates to a method for cleaning the semiconductor substrate surface by using said cleaning agent.
At present, according to the recent trend of high integration of LSI, various technologies have been introduced in production steps of semiconductors. Silicon wafers, which are used for producing semiconductor devices mainly applied to production of LSIs, are prepared by cutting out from a single crystal of silicon ingot and being subjected to production steps of lapping and polishing. For these reasons, the surface of thus prepared silicon wafers are contaminated with a large amount of metallic impurities. Furthermore, in steps following to these production steps, the silicon wafer's surface may have a number of risks of metallic contamination, because the wafers are subjected to production steps of semiconductor devices such as ion implantation step, metal terminal formation step and etc.
In the recent years, it has have been proposed to introduce chemical mechanical polishing (CMP) technologies for producing the semiconductor devices in accordance with the requirement of planarization of the semiconductor substrate surface due to the recent trend of multi-level metallized wirings. The CMP technology is a method to make the surface of silicon wafers flat by using a slurry of silica or alumina. The objectives of polishing are silicon oxide film, wirings and plugs on the surface. In this case, the surface of silicon wafers is contaminated with silica or alumina slurry, metallic impurities contained in the slurries, and metallic impurities caused by polished plug or wiring metals. In such a case, a large amount of metallic contaminants are widely spreaded out on the whole surface of the silicon wafers.
When the semiconductor substrate surface is contaminated with metallic impurities as mentioned above, the electrical properties of semiconductor devices are affected for the worse, and as a result the reliability of semiconductor devices will be lowered. Further, the semiconductor device may possibly be destroyed for a large amount of metallic contamination. So that it is necessary to remove the metallic contaminants from the substrate surface by introducing a cleaning step after the CMP process.
Nowadays, the cleaning step is conducted by a method of chemical cleaning, physical cleaning or combinations thereof. Among methods of chemical cleaning, RCA cleaning method which was developed in the 1970's, is used widely in the art. The solution of RCA cleaning is consisting of acid-type cleaning solutions and alkali-type cleaning solutions. The acid-type cleaning solution, such as HPM (hydrochloric acid-hydrogen peroxide mixed aqueous solution) and DHF (diluted hydrofluoric acid solution) is used for removing the metallic contaminants. On the other hand, the alkali type cleaning solution, which is represented by APM (ammonia-hydrogen peroxide mixed aqueous solution), possesses an excellent ability to remove the particle contaminants, but it possesses insufficient ability to remove the metallic contaminants.
Under such circumstances, for the purpose to remove the metallic contaminants, the acid-type cleaning solution such as HPM and DHF may inevitably be used.
However, the metallized wirings being provided on the semiconductor substrate surface may be corroded with the cleaning solution, because such an acid-type cleaning solution possesses strong ability to dissolve the metals.
In order to avoid such corrosion problem of the metallized wirings being provided on the semiconductor substrate surface, a physical (mechanical) cleaning method can be applied. As to the physical cleaning method, there can be exemplified by a brush-scrubbing method by using high speed rotating brush(s); an ice-scrubbing method by using jetted out fine particles of ice; a method of cleaning by high pressure jet stream of ultra-pure water; and a megasonic cleaning method by using ultrasonic wave and the like.
Each one of these physical cleaning methods is effective to avoid corrosion problem of the metallized wirings being provided on the semiconductor substrate surface. However, the ability for removing metallic contaminants can hardly be expected only by use of these physical cleaning methods. For this reason, it is proposed to use the physical cleaning method in combination with chemical cleaning method by using an acid-type cleaning solution.
It should be noted that though the ability for removing metallic contaminants can be expected by conducting the RCA cleaning method using an inorganic acid, such method has some problems exemplified that the metallized wirings being provided on the surface may be damaged, further the insulation film of silicon oxide being provided on the surface may be etched with the inorganic acid.
Therefore, it is necessary to dilute the concentration of the inorganic acid as low as possible, and to reduce the cleaning time as short as possible.
However, as a result of such considerations, adequate effects for cleaning can not be expected.
In addition to the above, another method for cleaning the semiconductor substrate surface is available, in which an aqueous solution of a monocarboxylic acid in combination with a surfactant is used. However, this method is understood that though it is effective to improve the wettability between the aqueous solution and the semiconductor substrate surface by use of the surfactant, this method requires the longer time to remove the metallic contaminants, further an adequate cleaning efficiency can not be expected.
Additionally, another method for removing the metallic contaminants such as the one using citric acid solution in combination with a brush-scrubbing cleaning was reported. However, the effect for removing the metallic contaminants was insufficient only by use of citric acid solution, so that an adequate cleaning effects was not obtained.
As explained above, there have not, been found yet any effective means for removing particles and metallic contaminants without corroding the metallized wirings and without giving adverse effect of planarization on the semiconductor substrate surface.